Enum changed to NSENUM to support Swift
Enum changed to NSENUM to support Swift

cooksimo/TWMessageBarManager,VojtaStavik/TWMessageBarManager,CharlyInc/TWMessageBarManager,zuojx1013/TWMessageBarManager,AlexanderMazaletskiy/TWMessageBarManager,bobqian1130/TWMessageBarManager,terryworona/TWMessageBarManager,primoz990/TWMessageBarManager,revile/TWMessageBarManager,howeguo/TWMessageBarManager